| Several silicates containing ferric iron are known in a natural state, chief among which are Anthosiderite, 2Fe2O3.9SiO2. 2H2O; Cronstedtite, 3FeO.Fe2O3.2SiO2.3H2O; Hisingerite, 4Fe2O3.9SiO2. 18H2O; and Nontronite, Fe2O3.3SiO2.5H2O. A sodium ferric metasilicate occurs as Crocidolite, 2NaFe•••(SiO3)2.Fe••SiO3.Na2SiO3. |